1. Field of the Invention
The present invention relates, in general, to methods and devices for selectively passing image streams to a viewer of projected images, and, more particularly, to shuttered glasses or other optical filter devices that increase the number of video streams, e.g., two dimensional (2D) or three dimensional image streams, that may be viewed by a user of the shuttered glasses or other optical filter devices.
2. Relevant Background
Technologies presently exist that allow for multiple video or image streams to be broadcast or displayed on a single display or screen. For example, multiple image streams may be provided by projecting time multiplexed images onto a display screen and then synchronizing shuttered glasses to the time sequence corresponding to the frames displaying the desired image (e.g., the image to be seen at a particular time through the shuttered glasses). Glasses that can shutter at up to 300 Hertz are currently available and can be used to view at least three separate three dimensional (3D) streams or up to at least six separate two dimensional (2D) streams that are projected or displayed onto the same screen.
In most applications, multiple stream projection is used either to create a 3D effect (e.g., shuttering to control left and right eye images viewed by a person wearing the shuttered glasses) or to support multiple players in a video game environment. In the latter application, each player wears shuttered glasses that operate at a frequency such that they view an image stream associated with their player view such that split screen views are not required. For example, Player A and Player B using a video game system each wear glasses set to operate at differing frequencies such that they view a Player A video stream and a Player B video stream, respectively, as it is displayed in an alternating (or time multiplexed fashion) on the entire monitor or television screen.
In more recent developments, multiple video streams are projected on a display surface and each viewer or subsets of viewers are able to choose which video stream is viewed by modifying the shuttered glasses or other optical filters. For example, shuttered glasses may be provided to each of the audience members and two or more video streams projected on a theater screen. The shuttered glasses include a switching capability that allows them to be operated at two or more operating states (e.g., frequencies, polarization state of the polarized filter, or the like) to synchronize shuttering to view any of the projected video streams. In some cases, a guest controlled action or audience member input (“user input”) is used to determine when to switch the shuttered glasses to a different operational state and to allow the audience member wearing the glasses to view a different video stream corresponding to the new operational state. In other cases, the switching may be controlled remotely based on the user input (e.g., audience members that lean left see a different image than those that lean right) or to achieve a desired effect (e.g., switching portions of the audience's optical filters or glasses to view differing streams during the particular event or game). Generally, the switching is immediate upon receipt of user input (or controller commands) to provide improved responsiveness and to increase the audience member's perception that they controlled the displayed image, but, in some cases, the response may be delayed such as to wait until a branch in a storyline or the like.
With the growing use of multi-viewer systems, there is a demand for more and more views or image streams to be available for viewing, e.g., more than the typically available three 3D image streams or six 2D image streams. In a multi-viewer system, the capabilities of the system may be limited and/or defined by the number of separable images or image streams. The number of separable images, for example, determines the number of different views, branches, and inter-positional steps that can be reproduced for individual viewers. To improve the capabilities of the multi-viewer system, there is a demand to increase the number of separable images.
In an active multi-viewer system (e.g., a system using time-synchronized shutter glasses), each frame is divided into time slots with a single image displayed in each time slot. The number of time slots and, therefore, images is limited by the response time of the shutter glasses (e.g., the shutter rate technology) and the desired projection frame rate. Further, simply increasing the shuttering frequencies to display more images may have limitations as this may result in the viewer seeing or sensing ghosting of sequentially displayed images (e.g., the left eye image may bleed into the right eye image viewing, a first 2D image stream may ghost into a second 2D image stream and so on). Within a single projection frame, time slots are defined for each separable image, and the shutter glasses must “open” and “close” in synchronization with the desired image. In the case of 3D systems, images are created by displaying the image for the left eye and the image for the right eye in different time slots and synchronizing the lenses of the shutter glasses with the time slot appropriate for each eye. Therefore, two time slots are needed to produce a single 3D image.
To better understand limitations on the number of separable images or image streams, it may be useful to look further at existing shutter glasses such as conventional liquid crystal display (LCD) shutter glasses. FIG. 1 illustrates an image stream 100 that may be used to present multiple image streams to viewers or audience members wearing shuttered glasses. Using the video or image stream 100, a set of images 112, 114, 116 are projected in a first frame 110 and a different set of images 122, 124, 126 are provided in a second frame 120. For example, a shuttered video projector (or three shuttered video projectors) may be used to provide three differing video streams or separable images on a single display, with viewers using their synchronized shutter glasses to view one of the images (e.g., one viewer may view Image 1 by viewing only images 112, 122 in successive frames while another viewer may view Image 3 by viewing only images 116, 126 in successive frames). Multiple images are projected or displayed in stream 100 for each frame 110, 120 with individual images separated by displaying each image only during a specific time slot within the time frame 110, 120 (e.g., images 112, 122 associated with Image 1 are only displayed during the first sub-frame time slot of each frame 110, 120). As shown, one image is displayed or provided in the stream 100 in each time slot of the frames 110, 120. The number of time slots and, therefore, the number of separable images is limited by the response times of the display system and the viewing mechanism such as LCD shutter glasses or other optical filter. Typically, only two time slots are used in a stream rather than the three shown in FIG. 1, but research suggests that up to six time slots may be feasible in each frame 110, 120 with existing projection and viewing technologies. However, there are proposed uses of image streams with up to 6 to 12 or more separable images. Hence, existing technology is not able to meet increasing demands for more and more separable images (or time slots per frame).
Regarding separation of these displayed or projected images, an individual image is presented to each viewer in conventional viewing mechanisms by providing a switchable optical shutter that is synchronized to open only during the time slot corresponding to the desired image. For example, LCD shutter glasses may be used, and these devices typically include a pair of lenses containing liquid crystal and a pair of polarizing filters. Each lens may be adapted to become dark when voltage is applied but otherwise be transparent (or vice versa). FIG. 2 illustrates one multi-image viewing/display system 200 (such as may be used in a theater, a video game setting, or the like) using LCD shutter glasses 230 to view one of a number of separable images. An image source 210 is used to provide an image stream 220 to the LCD shutter glasses 230, which would be worn by each viewer or member of an audience. The image source 210 may be a monitor or display surface upon which a projector, a computer video system, or the like may provide a stream of image frames with two or more image streams (such as shown in FIG. 1).
The light or image stream 220 from the image source 210 is shown to be unpolarized light. The LCD shutter glasses 230 include two lenses in this example with each being formed with a switchable optical rotator (i.e., the liquid crystal portion) 234, 242 sandwiched between a pair of polarized filters 232, 236, 240, 244. In the illustrated system 200, the LCD shutter glasses 230 are in an operating state with the optical filter 242 associated with the left eye energized such that the left lens is dark and no light passes to the left eye as shown at 245. Different operating states are created by selectively energizing one or both of the optical rotators 234, 242 to allow light to pass to the viewer's eyes 238, 246, and, in this manner, the viewer is able to see only one of multiple images provided in a particular frame (e.g., images associated with a particular time slot of each sequential time frame).
As shown in FIG. 2, light 220 passes through a first polarization filter 232, 240 in each lens to create polarized light 233, 241. Then, the light 233, 241 next passes through a switchable optical rotator 234, 242. Typically, the optical rotator 234, 242 is made up of a twisted nematic liquid crystal, and in use, if the switchable optical rotator 234, 242 is energized as shown for rotator 242 the light 243 passes without rotation. If the switchable optical rotator 234, 242 is not energized as shown for rotator 234, the polarized light 235 is rotated by 90 degrees as it is passed through the rotator 234. Therefore, after passing through the first polarization filter 232 or 240 and the switchable optical rotator 234 or 242, the light 235, 243 is polarized in one of two orthogonal orientations, with the orientation depending on whether or not the switchable optical rotator 234, 242 is energized (e.g., by voltage selectively provided by a power source operated by a controller to synchronize shuttering with an image stream provided via image source 210).
The light 235, 243 then encounters a second polarization filter 236, 244 that is aligned with one of the two orthogonal polarization axes created by passing through the first polarization filter 232, 240 and the switchable rotator 234, 244. If the light 235 incident on the second polarization filter 236 is aligned with the polarization axis of the filter the light 237 is passed through the LCD shutter glass lens (here to the right eye). If the light 243 incident on the second polarization filter 244 is orthogonal to the polarization axis of the filter the light is blocked, as shown at 245 for the left eye of the viewer. Selection between 2D images is accomplished through use of the LCD shutter glasses 230 by synchronizing the switchable optical rotators 234 and 242 such that the left and right eye shutters or lenses are synchronized with the same time slot of an image stream frame (again, see FIG. 1, for examples of multiple images being projected in each time frame). If the stream 220 is used to present 3D images, selection between 3D images is accomplished by synchronizing the switchable optical rotator 234, 242 such that the left and right eye shutters are synchronized with different time slots within a time frame. For example, as shown in FIG. 2, one image 237 may represent the image for the right eye 238 that is presented in a first time slot and one image 245 may represent the image for the left eye 246 in a second time slot.
The number of different images that can be presented to a viewer depends on the number of time slots available in each frame of a video stream, with one time slot being needed for each 2D image and two times slots being needed for each 3D image. For example, a video stream may include frames that each includes six time slots (e.g., an upper limit typically believed achievable with existing viewing mechanisms such as LCD shutter glasses and the like). In this case, the number of separable images or image streams that could be represented is up to six 2D images (i.e., 6 time slots/1 time slot per image=6 images) and up to three 3D images (i.e., 6 time slots/2 time slots per image=3 images).
Hence, there remains a need for improved methods and devices for allowing larger numbers of separable images or image streams to be presented to viewers. Preferably, such methods and devices would allow viewers to view one of many separable images projected or displayed in a multi-viewer theatre or other application or in a multi-player video game. Such applications may be designed for presenting more than three 3D images, and, more particularly, may be designed for presenting more than six 2D images or image streams to viewers.